The heat is not helping, but I don’t think the only factor at play here. Why did you decide to fertigate so often? You probably only need to be doing one a day right now and could up it to twice a day if the flowers start to develop more. Very high frequency fertigation is really only necessary in pretty specific circumstances, and otherwise can be detrimental. Coco can be a lot wetter than soil but in general it shouldn’t be soaked all the time.
Plants also look kinda stretchy, how many watts is your light and how high is it from the plants? Do you possibly have a light leak keeping them from fully flowering?